Method for controlling a flowrate of a recirculated exhaust gas

ABSTRACT

A method for controlling an exhaust gas recirculation (EGR) system is provided. The EGR system may allow for the removal and the sequestration of at least one constituent within the exhaust before the recirculation occurs. The method may monitor the level of at least one constituent and adjust an EGR recirculation rate.

This application is related to commonly-assigned U.S. patent application Ser. No. 11/928,038 [GE Docket 227348], filed Oct. 30, 2007; U.S. patent application Ser. No. 11/953,524 [GE Docket 228179], filed Dec. 10, 2007; and U.S. patent application Ser. No. 11/953,556 [GE Docket 229334], filed Dec. 10, 2007.

BACKGROUND OF THE INVENTION

The present invention relates to an exhaust gas recirculation system, and more particularly to a method and system for controlling the quantity of exhaust reentering a turbomachine after processing by a recirculation system.

There is a growing concern over the long-term effects of Nitrogen Oxides (hereinafter NOx) and Carbon Dioxide (hereinafter “CO₂”) and Sulfur Oxides (SOx) emissions on the environment. The allowable levels of emissions that may be emitted by a turbomachine, such as a gas turbine, are heavily regulated. Operators of turbomachines desire methods of reducing the levels of NOx, CO₂, and SOx emitted.

Significant amounts of condensable vapors exist in the exhaust gas stream. These vapors usually contain a variety of constituents such as water, acids, aldehydes, hydrocarbons, sulfur oxides, and chlorine compounds. Left untreated, these constituents will accelerate corrosion and fouling of the internal components if allowed to enter the turbomachine.

Exhaust gas recirculation (EGR) generally involves recirculating a portion of the emitted exhaust through an inlet portion of the turbomachine. The exhaust is then mixed with the incoming airflow prior to combustion. The EGR process facilitates the removal and sequestration of concentrated CO₂, and may also reduce the NOx and SOx emission levels.

There are a few concerns with the currently known EGR systems. The quantity and rate of the recirculated exhaust impacts the turbomachine operability including, but not limiting of: combustor stability, emissions, compressor stability, and component life.

For the foregoing reasons, there is a need for a method and system for controlling the composition of the inlet fluid exiting the EGR system. The method and system should control the flow rate of exhaust reentering the turbomachine. The method and system should use a flowrate of the recirculated exhaust as a control parameter. The method and system should reduce the sensitivity of the EGR system to varying fuel compositions.

BRIEF DESCRIPTION OF THE INVENTION

In accordance with an embodiment of the present invention, a method of controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the method comprising: providing at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device and at least one flow control device; utilizing a mass flow control system, wherein utilizing the mass flow control comprises the steps of: receiving a target EGR fraction comprising the portion of the exhaust stream within an inlet fluid, wherein the inlet fluid enters the inlet section of the turbomachine; determining a current EGR fraction; determining whether the current EGR fraction is within a range of the target EGR fraction; and adjusting an EGR rate of the exhaust stream if the current EGR fraction is outside of the range of the target EGR fraction.

In accordance with an alternate embodiment of the present invention, a method of controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the method comprising: providing at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device and at least one flow control device; utilizing a mass flow control system, wherein the utilizing the mass flow control comprises the steps of: receiving a target level of at least one constituent; determining a target EGR fraction; determining a current EGR fraction; determining whether the current EGR fraction is within a range of the target EGR fraction; and adjusting an EGR rate of the exhaust stream if the current EGR fraction is outside of the range of the target EGR fraction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustrating the environment in which an embodiment of the present invention operates.

FIG. 2 is a flowchart illustrating an example of a method of utilizing an EGR constituent control system in accordance with an embodiment of the present invention.

FIG. 3 is a flowchart illustrating an example of a method of utilizing an EGR mass flow control system in accordance with an embodiment of the present invention.

FIG. 4 is a flowchart illustrating an example of a method of utilizing an EGR constituent control system in accordance with an alternate embodiment of the present invention.

FIG. 5 is a flowchart illustrating an example of a method of utilizing an EGR mass flow control system in accordance with an alternate embodiment of the present invention.

FIG. 6 is a block diagram of an exemplary system for adjusting an EGR rate in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description of preferred embodiments refers to the accompanying drawings, which illustrate specific embodiments of the invention. Other embodiments having different structures and operations do not depart from the scope of the present invention.

Certain terminology is used herein for the convenience of the reader only and is not to be taken as a limitation on the scope of the invention. For example, words such as “upper,” “lower,” “left,” “right,” “front”, “rear” “top”, “bottom”, “horizontal,” “vertical,” “upstream,” “downstream,” “fore”, “aft”, and the like; merely describe the configuration shown in the Figures. Indeed, the element or elements of an embodiment of the present invention may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise.

An EGR rate may be considered the rate and quantity of exhaust stream that enters the inlet section of the turbomachine. The composition of the inlet fluid includes, but is not limiting of, the exhaust stream, the inlet air, and at least one of the aforementioned constituents, and combinations thereof.

The present invention may be applied to the variety of turbomachines that produce a gaseous fluid, such as, but not limiting of, a heavy duty gas turbine; an aero-derivative gas turbine: or the like (hereinafter referred to as “gas turbine”). An embodiment of the present invention may be applied to either a single gas turbine or a plurality of gas turbines. An embodiment of the present invention may be applied to a gas turbine operating in a simple cycle or a combined cycle configuration.

Referring now to the Figures, where the various numbers represent like elements throughout the several views, FIG. 1 is a schematic illustrating the environment in which an embodiment of the present invention operates. FIG. 1 illustrates a site 100, such as but not limiting of a powerplant site, having a turbomachine 105, an EGR system 107, a heat recovery steam generator (HRSG) 155, and an exhaust stack 165. Alternatively, the present invention may be integrated with a site 100 not having the HRSG 155.

The EGR system 107 comprises multiple elements. The configuration and sequence of these elements may be dictated by the composition of the exhaust stream 170 and the type of cooling fluid used by the components of the EGR system 107. Furthermore, alternate embodiments of the EGR system 107 may include additional or fewer components than the components described below. Therefore, various arrangements, and/or configurations, which differ from FIG. 1, may be integrated with an embodiment of the present invention.

As illustrated in FIG. 1, the EGR system 107 comprises: a mixing station 115, an inlet modulation device 120, a bypass modulation device 125, a bypass stack 130, at least one EGR flow conditioning device 135, a downstream temperature conditioning device 140, a constituent reduction system 145, an upstream temperature conditioning device 150, at least one exhaust modulation device 160, and at least one EGR feedback device 175. The at least one EGR feedback device 175 may provide direct or indirect data on at least one of: the current EGR flowrate; the concentration of at least one constituent, or combinations thereof.

Generally, the process used by the EGR system 107 may include: cooling of the exhaust stream 170; reduction and removal of the aforementioned constituents within the exhaust stream 170; and then mixing the exhaust stream 170 with the inlet air, forming an inlet fluid; which flows from the inlet section 110 through to the exhaust stack 165. The EGR system 107 may reduce the temperature of the exhaust stream 170 to a saturation temperature where the aforementioned constituents may condense and then be removed. Alternatively, the EGR system 107 may also reduce the temperature of, and use a scrubbing process (or the like) on, the exhaust stream 170 to remove the aforementioned constituents.

While EGR system 107 operates, the at least one EGR feedback device 175 may determine the flowrate of the exhaust stream 170, which may be used to determine the EGR fraction. The at least one EGR feedback device 175 may be located adjacent the inlet section 110 of the turbomachine 105. The at least one EGR feedback device 175 may be used to determine the concentration of at least one constituent within the inlet fluid.

As will be appreciated, the present invention may be embodied as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects all generally referred to herein as a “circuit”, “module,” or “system”. Furthermore, the present invention may take the form of a computer program product on a computer-usable storage medium having computer-usable program code embodied in the medium.

Any suitable computer readable medium may be utilized. The computer-usable or computer-readable medium may be, for example but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. More specific examples (a non exhaustive list) of the computer-readable medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a transmission media such as those supporting the Internet or an intranet, or a magnetic storage device. Note that the computer-usable or computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via, for instance, optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory. In the context of this document, a computer-usable or computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.

Computer program code for carrying out operations of the present invention may be written in an object oriented programming language such as Java7, Smalltalk or C++, or the like. However, the computer program code for carrying out operations of the present invention may also be written in conventional procedural programming languages, such as the “C” programming language, or a similar language. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer. In the latter scenario, the remote computer may be connected to the user's computer through a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

The present invention is described below with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a public purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

The present invention has the technical effect of controlling the composition of an inlet fluid, which may be considered the working fluid, exiting an EGR system and entering the inlet portion of a turbomachine.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions, which execute on the computer or other programmable, provide steps for implementing the functions/acts specified in the flowchart and/or block diagram block.

The present invention may be configured to automatically or continuously monitor the inlet fluid of the turbomachine 105 to determine the quantity of the exhaust stream 170 that should enter the inlet section 110. Alternatively, the control system may be configured to require a user action to the initiate operation. An embodiment of the control system of the present invention may function as a stand-alone system. Alternatively, the control system may be integrated as a module, or the like, within a broader system, such as a turbine control or a plant control system. For example, but not limiting of, the control system of the present invention may be integrated with the control system operating the EGR system 107.

Referring now to FIG. 2, which is a flowchart illustrating an example of a method 200 of utilizing an EGR constituent control system in accordance with an embodiment of the present invention. The method 200 may include at least one EGR constituent control system, which may function, for example, but not limiting of, in steps 210 to 260. In an embodiment of the present invention the EGR system 107 may be integrated with a graphical user interface (GUI), or the like. The GUI may allow the operator to navigate through the method 200 described below. The GUI may also provide at least one notification of the status of the EGR system 107.

In step 210, of the method 200, the EGR system 107 may be processing an exhaust stream 170, as described. Depending on either the type and/or operation of the turbomachine 105, the generated exhaust may have a flowrate of about 10,000 Lb/hr to about 50,000,000 Lb/hr and a temperature of about 100 Degrees Fahrenheit to about 1,100 Degrees Fahrenheit.

In step 220, the method 200 may receive a target EGR fraction. The EGR fraction may be considered the flowrate of the exhaust stream 121. Alternatively, may be considered the amount, such as, but not limiting of, a percentage of the exhaust stream 170 within the inlet fluid. Here, the EGR fraction may be determined by dividing the mass flowrate of the exhaust stream 170 by the mass flowrate of the inlet air.

In an embodiment of the present invention, the method 200 may automatically receive the EGR fraction from the control system operating the EGR system 107. In an alternate of the present invention, a user may enter the EGR fraction.

In step 230, the method 200 may determine the target level of at least one constituent. The method 200 may utilize a species conservation engine, or the like, to determine the target level. The species conservation engine may incorporate a plurality of turbomachine operating data along with the target EGR fraction to calculate the target level. The plurality of turbomachine operating data may include: at least one fuel composition; the compressor airflow of the turbomachine 105; and the fuel flow of the turbomachine 105. The at least one fuel composition may include, but are not limited to: the composition of the fuel entering a combustion system of the turbomachine 105; and the composition of the fuel used in an auxiliary filing system integrated with the turbomachine 105, wherein the auxiliary filing system may include an auxiliary boiler, or combinations thereof.

The species conservation engine may incorporate a physical equation, or the like, to calculate the target level of at least one constituent. As discussed, the at least one constituent includes at least one of: SOx, NOx, CO₂, O₂, water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof.

The species conservation engine may incorporate a physical equation, or the like, to calculate the target level of at least one constituent. For example, but not limiting of, the species conservation engine may calculate a target exhaust CO, mole fraction as a function of: a target EGR mass fraction, fuel flow, fuel composition, and turbomachine 105 inlet flow. The target exhaust CO₂ mole fraction value may be compared to a CO₂ mole fraction measured by the at least one EGR feedback device 175. The comparison process may yield an error signal, which the method 200 may use for feedback control of the EGR flow rate.

Additionally, the combustion reaction for the turbomachine 105 that burns a hydrocarbon fuel in standard air may be described by Equation 1, using molar coefficients, as illustrated below:

C_(α)H_(γ)+(a+e)(O2+3.76N2)

bCO2+cH2o+eO2+(a+e)(3.76)N2  [Equation 1]

Here, “fuel composition” is defined by the carbon and hydrogen subscripts, α and γ. The excess oxygen molar coefficient, e, may be calculated as a function of EGR mass fraction (X_(EGR)), compressor inlet mass flow (W_(C)) and fuel mass flow (W_(F)) as illustrated by Equation 2.

$\begin{matrix} {e = {{\frac{1}{4.76}\frac{W_{C}\left( {1 - X_{EGR}} \right)}{W_{F}}\frac{{MW}_{fuel}}{{MW}_{air}}} - \left( {\alpha + {\gamma/4}} \right)}} & {{Equation}\mspace{14mu} 2} \end{matrix}$

The target exhaust CO₂ mole fraction (y_(CO2) _(—) _(target)), on a dry basis, may be calculated from the reaction in Equation 1 according to Equation 3.

$\begin{matrix} {y_{{CO}_{2}{\_ {target}}} = \frac{\alpha}{\alpha + e + {\left( {\alpha + {\gamma/4} + e} \right)(3.76)}}} & {{Equation}\mspace{14mu} 3} \end{matrix}$

Equations 1 through 3 may be adapted to perform similar species conservation calculations for constituents other than CO₂ or for a turbomachine 105 operating with different working fluids or fuel types. As discussed, the constituent includes at least one of: SOx, NOx. CO₂, O₂, water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof.

In step 240, the method 200 may determine the current level of at least one constituent. As discussed, the EGR system 107 may include the at least one EGR feedback device 175. The at least one EGR feedback device 175 may include sensors, transmitters, and similar devices that may provide data on the current level of the at least one constituent. The position of the at least one EGR feedback device 175 may provide feedback on the composition of the inlet fluid. The at least one EGR feedback device 175 may be located upstream and/or downstream of the combustion system of the turbomachine 105, increasing the accuracy of the feedback. The at least one EGR feedback device 175 may be integrated with the control system used to operate the method 200. The data provided by the at least one EGR feedback device 175 may be used to directly or indirectly determine the current level of at least one constituent.

In step 250, the method 900 may determine whether the current level of the at least one constituent is within a constituent range. Here, the method 200 compares the target level determined in step 230, and the current level determined in step 240 of the at least one constituent. In an embodiment of the present invention, an operator may determine the range. In an alternate embodiment of the present invention, the range may be automatically determined. For example, but not limiting of, if the target level is 1 and the current level is from about 0.95 to about 1.05, then the method 200 may determine that the current level of the at least one constituent is within range.

Additionally, for example, but not limiting of, the turbomachine 105 may be operated with a target EGR mass fraction of 30%, a fuel/compressor inlet flow ratio near 0.019 and a fuel composition of 97% methane (CH4), 2% ethane (C2H6) and 1% propane (C3H8) which yields a target exhaust CO₂ mole fraction (dry) of 0.051. The method 200 may adjust the EGR flow rate to maintain the measured exhaust CO₂ mole fraction (dry) within +/−0.001 of the target, over a range of measured CO₂ mole fractions from 0.005 to 0.25.

If the level of at least one constituent is outside of the range then the method 200 may proceed to step 260; otherwise the method 200 may revert to step 210 where the steps 210-250 may repeat until the at least one constituent is outside of the range.

In step 260, the method 200 may adjust an EGR rate. As discussed, the EGR rate may be considered the rate and quantity of exhaust stream 170 entering the mixing station 115 where the inlet fluid is created. In an embodiment of the present invention, the method 200 may repeat steps 210-260 to confirm that the at least one constituent remains within the aforementioned range.

An embodiment of the present invention may utilize the components of the EGR system 107 to adjust the EGR rate. For example, but not limiting of, the method 200 may incorporate at least one of the following functions: adjusting a speed of an EGR flow conditioning device 135, such as but not limiting of an EGR fan speed; adjusting a pitch of at least one EGR fan blade; modulating at least one flow control device. The flow control device may include at least one of: an inlet damper, a bypass damper, an exhaust damper, or combinations thereof.

In an embodiment of the present invention, the GUI may provide a notification to the user if the EGR rate should be adjusted.

FIG. 3 is a flowchart illustrating an example of a method 300 of controlling the EGR rate of an inlet fluid in accordance with an embodiment of the present invention. The method 300 may include at least one EGR mass flow control system, which may function, for example, but not limiting of, in steps 310 to 350 below. In an embodiment of the present invention the EGR system 107 may be integrated with a graphical user interface (GUI), or the like. The GUI may allow the operator to navigate through the method 300 described below. The GUI may also provide at least one notification of the status of the EGR system 107.

In step 310, of the method 300, the EGR system 107 may be processing an exhaust stream 170, as described. As discussed, the generated exhaust may have a flowrate of about 10,000 Lb/hr to about 50,000,000 Lb/hr and a temperature of about 100 Degrees Fahrenheit to about 1,100 Degrees Fahrenheit.

In step 320, the method 300 may receive a target EGR fraction. The EGR fraction may be considered the amount, such as, but not limiting of, a percentage of the exhaust stream 170 within the inlet fluid. EGR fraction may be determined by dividing the mass flowrate of the exhaust stream 170 by the mass flowrate of the inlet air. In an embodiment of the present invention, the method 300 may automatically receive the EGR fraction from the control system operating the EGR system 107. In an alternate embodiment of the present invention, a user may enter the EGR fraction.

In step 330, the method 300 may determine the current EGR fraction. An embodiment of the present invention may receive the current EGR rate data from the at least one EGR feedback device 175. The at least one EGR feedback device 175 may include sensors, transmitters, and similar devices that may provide data on the current flow rate of the exhaust stream 170. The EGR rate data may be used to determine the EGR fraction. In an alternate embodiment of the present invention at least one energy balance may be used to determine the current EGR fraction.

The energy balance is generally based on the Conservation of Energy, which generally states that the energy entering a system equals the energy exiting the same system. The energy balance of an embodiment of the present invention is illustrated in Equation 4, which may be solved for W_(EGR) that may be used to determine the EGR fraction.

$\begin{matrix} {W_{EGR} = \frac{W_{Tin}\begin{pmatrix} {{C_{P\_ Tin}\left( {T_{Tin} - T_{ref}} \right)} -} \\ {C_{P\_ air}\left( {T_{air} - T_{ref}} \right)} \end{pmatrix}}{{C_{P\_ EGR}\left( {T_{EGR} - T_{ref}} \right)} - {C_{P\_ air}\left( {T_{air} - T_{ref}} \right)}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack \end{matrix}$

where: W_(EGR) is the flowrate of exhaust stream 170; T_(EGR) is the temperature of exhaust stream 170; C_(P) _(—) _(EGR) is the specific heat at constant pressure of the exhaust stream 170; W_(Tin) is the total flowrate into the turbomachine inlet; T_(Tin) is the temperature of the turbomachine inlet flow; C_(P) _(—) _(Tin) is the specific heat at constant pressure of the turbomachine inlet flow; T_(air) is the temperature of the ambient air; C_(P) _(—) _(air) is the specific heat at constant pressure of the ambient air; and T_(ref) is a reference temperature for calculating absolute enthalpy.

In step 340, the method 300 may determine whether the current EGR fraction is within a range of the target EGR fraction. Here, the method 300 compares the target EGR fraction determined in step 320, and the current EGR fraction determined in step 330. In an embodiment of the present invention an operator may determine the range, which may be a tolerance band or the like. In an alternate embodiment of the present invention the range may be automatically determined. For example, but not limiting of, if the target EGR fraction is 1 and the current EGR fraction is from about 0.95 to about 1.05, then the method 300 may determine that the current EGR fraction is within the range.

If the current EGR fraction is outside of the range then the method 300 may proceed to step 350; otherwise the method 300 may revert to step 310 where the steps 310-340 may repeat until the current EGR fraction is outside of the range.

In step 350, the method 300 may adjust an EGR rate. As discussed, the EGR rate may be considered the rate and quantity of exhaust stream 170 entering the mixing station 115 where the inlet fluid is created. In an embodiment of the present invention, the method 300 may repeat steps 310-350 to confirm that the current EGR fraction is within the range of the target EGR fraction.

An embodiment of the present invention may utilize the components of the EGR system 107 to adjust the EGR rate. For example, but not limiting of, the method 300 may incorporate at least one of the following functions: adjusting a speed of an EGR flow conditioning device 135, such as, but not limiting of a source of air, where the source of air comprises a fan, a blower, or combinations thereof; adjusting a pitch of at least one EGR fan blade: modulating at least one flow control device. The flow control device may include at least one of: an inlet damper, a bypass damper, an exhaust damper, or combinations thereof. In an embodiment of the present invention, the GUI may provide a notification to the user if the EGR rate should be adjusted.

In an alternate embodiment of the present invention, the EGR mass flow control system of the method 300 may be integrated with the EGR constituent control system of the method 200. Generally, the EGR mass flow control system may provide a relatively faster response to the overall operation of the EGR system 107 than the constituent control system. However, the EGR constituent control system may provide a relatively more accurate feedback on the overall operation of the EGR system than the EGR mass flow control system. Therefore, integrating the EGR mass flow control system and the EGR constituent control system may provide for an initial fast feedback, followed by a slower and more accurate response to the overall operation of the EGR system 107.

FIG. 4 is a flowchart illustrating an example of a method 400 of utilizing an EGR constituent control system in accordance with an alternate embodiment of the present invention.

The method 400 may include at least one EGR constituent control system, which may function, for example, but not limiting of, in steps 410 to 450. In an embodiment of the present invention the EGR system 107 may be integrated with a graphical user interface (GUI), or the like. The GUI may allow the operator to navigate through the method 200 described below. The GUI may also provide at least one notification of the status of the EGR system 107.

In step 410, of the method 400, the EGR system 107 may be processing an exhaust stream 170, as described.

In step 420, the method 400 may receive a target level for at least one constituent. The target level for the at least one constituent may include an emissions limitation. For example, but not limiting of, the site 100 may operate under a NOx emissions limitation of 9 PPM. In an embodiment of the present invention, the method 400 may automatically receive the target level of the at least one constituent from the control system operating the EGR system 107 or the turbomachine 105. In an alternate of the present invention, a user may enter the target level for the at least one constituent. As discussed, the at least one constituent includes at least one of: SOx, NOx, CO₂, O₂, water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof.

In step 430, the method 400 may determine the current level of at least one constituent. As discussed, the EGR system 107 may include the at least one EGR feedback device 175. The at least one EGR feedback device 175 may include sensors, transmitters, and similar devices that may provide data on the current level of the at least one constituent. The position of the at least one EGR feedback device 175 may provide feedback on the composition of the inlet fluid. The at least one EGR feedback device 175 may be located upstream and/or downstream of the combustion system of the turbomachine 105, increasing the accuracy of the feedback. The at least one EGR feedback device 175 may be integrated with the control system used to operate the method 400. The data provided by the at least one EGR feedback device 175 may be used to directly or indirectly determine the current level of at least one constituent.

In step 440, the method 400 may determine whether the current level of the at least one constituent is within a constituent range. Here, the method 400 compares the target constituent level received in step 420, and the current level determined in step 430 of the at least one constituent. In an embodiment of the present invention, an operator may determine the range. In an alternate embodiment of the present invention, the range may be automatically determined. For example, but not limiting of, if the target level is 1 and the current level is from about 0.95 to about 1.05, then the method 400 may determine that the current level of the at least one constituent is within range.

Additionally, for example, but not limiting of, the turbomachine 105 may be operated with a target EGR mass fraction of 30%, a fuel/compressor inlet flow ratio near 0.019 and a fuel composition of 97% methane (CH4), 2% ethane (C2H6) and 1% propane (C3H8) which yields a target exhaust CO₂ mole fraction (dry) of 0.051. The method 400 may adjust the EGR flow rate to maintain the measured exhaust CO₂ mole fraction (dry) within +/−0.001 of the target, over a range of measured CO₂ mole fractions from 0.005 to 0.25.

If the level of at least one constituent is outside of the range then the method 400 may proceed to step 450; otherwise the method 400 may revert to step 410 where the steps 410-440 may repeat until the at least one constituent is outside of the range.

In step 450, the method 400 may adjust an EGR rate. As discussed, the EGR rate may be considered the rate and quantity of exhaust stream 170 entering the mixing station 115 where the inlet fluid is created. In an embodiment of the present invention, the method 400 may repeat steps 410-450 to confirm that the at least one constituent remains within the aforementioned range.

An embodiment of the present invention may utilize the components of the EGR system 107 to adjust the EGR rate. For example, but not limiting of, the method 200 may incorporate at least one of the following functions: adjusting a speed of an EGR flow conditioning device 135, such as but not limiting of an EGR fan speed; adjusting a pitch of at least one EGR fan blade; modulating at least one flow control device. The flow control device may include at least one of: an inlet damper, a bypass damper, an exhaust damper, or combinations thereof.

FIG. 5 is a flowchart illustrating an example of a method 500 of utilizing an EGR mass flow control system in accordance with an alternate embodiment of the present invention. The method 500 may include at least one EGR mass flow control system, which may function, for example, but not limiting of, in steps 510 to 560 below. In an embodiment of the present invention the EGR system 107 may be integrated with a graphical user interface (GUI), or the like. The GUI may allow the operator to navigate through the method 500 described below. The GUI may also provide at least one notification of the status of the EGR system 107.

In step 510, of the method 500, the EGR system 107 may be processing an exhaust stream 170, as described.

In step 520, the method 500 may receive a target level of at least one constituent. As discussed, the target level for the at least one constituent may include an emissions limitation. For example, but not limiting of, the site 100 may operate under a NOx emissions limitation of 9 PPM. In an embodiment of the present invention, the method 400 may automatically receive the target level of the at least one constituent from the control system operating the EGR system 107 or the turbomachine 105. In an alternate of the present invention, a user may enter the target level for the at least one constituent. As discussed, the at least one constituent includes at least one of: SOx, NOx, CO₂, O₂, water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof.

In step 530, the method 500 may utilized the aforementioned species conversion engine to determine a target EGR fraction. As discussed, the EGR fraction may be considered the amount, such as, but not limiting of, a percentage of the exhaust stream 170 within the inlet fluid. As discussed, EGR fraction may be determined by dividing the mass flowrate of the exhaust stream 170 by the mass flowrate of the inlet air.

In step 540, the method 500 may determine the current EGR fraction. An embodiment of the present invention may receive the current EGR rate data from the at least one EGR feedback device 175. The at least one EGR feedback device 175 may include sensors, transmitters, and similar devices that may provide data on the current flow rate of the exhaust stream 170. The EGR rate data may be used to determine the EGR fraction. In an alternate embodiment of the present invention the aforementioned energy balance may be used to determine the current EGR fraction.

In step 550, the method 500 may determine whether the current EGR fraction is within a range of the target EGR fraction. Here, the method 500 compares the target EGR fraction determined in step 530, and the current EGR fraction determined in step 540. In an embodiment of the present invention an operator may determine the range, which may be a tolerance band or the like. In an alternate embodiment of the present invention the range may be automatically determined. For example, but not limiting of, if the target EGR fraction is 1 and the current EGR fraction is from about 0.95 to about 1.05, then the method 500 may determine that the current EGR fraction is within the range.

If the level of at least one constituent is outside of the range then the method 500 may proceed to step 560; otherwise the method 500 may revert to step 510 where the steps 510-550 may repeat until the current EGR fraction is outside of the range.

In step 560, the method 500 may adjust an EGR rate. As discussed, the EGR rate may be considered the rate and quantity of exhaust stream 170 entering the mixing station 115 where the inlet fluid is created. In an embodiment of the present invention, the method 500 may repeat steps 510-560 to confirm that the current EGR fraction is within the range of the target EGR fraction.

An embodiment of the present invention may utilize the components of the EGR system 107 to adjust the EGR rate. For example, but not limiting of, the method 500 may incorporate at least one of the following functions: adjusting a speed of an EGR flow conditioning device 135, such as, but not limiting of a source of air, where the source of air comprises a fan, a blower, or combinations thereof; adjusting a pitch of at least one EGR fan blade; modulating at least one flow control device. The flow control device may include at least one of: an inlet damper, a bypass damper, an exhaust damper, or combinations thereof. In an embodiment of the present invention, the GUI may provide a notification to the user if the EGR rate should be adjusted.

In an alternate embodiment of the present invention, the EGR mass flow control system of the method 500 may be integrated with the EGR constituent control system of the method 400. Generally, the EGR mass flow control system may provide a relatively faster response to the overall operation of the EGR system 107 than the constituent control system. However, the EGR constituent control system may provide a relatively more accurate feedback on the overall operation of the EGR system than the EGR mass flow control system. Therefore, integrating the EGR mass flow control system and the EGR constituent control system may provide for an initial fast feedback, followed by a slower and more accurate response to the overall operation of the EGR system 107.

FIG. 6 is a block diagram of an exemplary system 600 for adjusting an EGR rate in accordance with an embodiment of the present invention. The elements of the methods 200, 300, 400 and 500 may be embodied in and performed by the system 600. The system 600 may include one or more user or client communication devices 602 or similar systems or devices (two are illustrated in FIG. 6). Each communication device 602 may be for example, but not limited to, a computer system, a personal digital assistant, a cellular phone, or similar device capable of sending and receiving an electronic message.

The communication device 602 may include a system memory 604 or local file system. The system memory 604 may include for example, but is not limited to, a read only memory (ROM), a random access memory (RAM), a flash memory, and other storage devices. The ROM may include a basic input/output system (BIOS). The BIOS may contain basic routines that help to transfer information between elements or components of the communication device 602. The system memory 604 may contain an operating system 606 to control overall operation of the communication device 602. The system memory 604 may also include a browser 608 or web browser. The system memory 604 may also include data structures 610 or computer-executable code for adjusting an EGR rate that may be similar or include elements of the methods 200, 300, 400, and 500 in FIGS. 2, 3, 4, and 5 respectively.

The system memory 604 may further include a template cache memory 612, which may be used in conjunction with the methods 200, 300, 400, and 500 in FIGS. 2, 3, 4, and 5 respectively, for adjusting an EGR rate.

The communication device 602 may also include a processor or processing unit 614 to control operations of the other components of the communication device 602. The operating system 606, browser 608, and data structures 610 may be operable on the processing unit 614. The processing unit 614 may be coupled to the memory system 604 and other components of the communication device 602 by a system bus 616.

The communication device 602 may also include multiple input devices (I/O), output devices or combination input/output devices 618. Each input/output device 618 may be coupled to the system bus 616 by an input/output interface (not shown in FIG. 6). The input and output devices or combination I/O devices 618 permit a user to operate and interface with the communication device 602 and to control operation of the browser 608 and data structures 610 to access, operate and control the software to adjust an EGR rate. The I/O devices 618 may include a keyboard and computer pointing device or the like to perform the operations discussed herein.

The I/O devices 618 may also include for example, but are not limited to, disk drives, optical, mechanical, magnetic, or infrared input/output devices, modems or the like. The I/O devices 618 may be used to access a storage medium 620. The medium 620 may contain, store, communicate, or transport computer-readable or computer-executable instructions or other information for use by or in connection with a system, such as the communication devices 602.

The communication device 602 may also include or be connected to other devices, such as a display or monitor 622. The monitor 622 may permit the user to interface with the communication device 602.

The communication device 602 may also include a hard drive 624. The hard drive 624 may be coupled to the system bus 616 by a hard drive interface (not shown in FIG. 6). The hard drive 624 may also form part of the local file system or system memory 604. Programs, software, and data may be transferred and exchanged between the system memory 604 and the hard drive 624 for operation of the communication device 602.

The communication device 602 may communicate with at least one unit controller 626 and may access other servers or other communication devices similar to communication device 602 via a network 628. The system bus 616 may be coupled to the network 628 by a network interface 630. The network interface 630 may be a modem, Ethernet card, router, gateway, or the like for coupling to the network 628. The coupling may be a wired or wireless connection. The network 628 may be the Internet, private network, an intranet, or the like.

The at least one unit controller 626 may also include a system memory 632 that may include a file system, ROM, RAM, and the like. The system memory 632 may include an operating system 634 similar to operating system 606 in communication devices 602. The system memory 632 may also include data structures 636 for adjusting an EGR rate. The data structures 636 may include operations similar to those described with respect to the methods 200, 300, 400 and 500, respectively for adjusting an EGR rate. The server system memory 632 may also include other files 638, applications, modules, and the like.

The at least one unit controller 626 may also include a processor 642 or a processing unit to control operation of other devices in the at least one unit controller 626. The at least one unit controller 626 may also include I/O device 644. The I/O devices 644 may be similar to I/O devices 618 of communication devices 602. The at least one unit controller 626 may further include other devices 646, such as a monitor or the like to provide an interface along with the I/O devices 644 to the at least one unit controller 626. The at least one unit controller 626 may also include a hard disk drive 648. A system bus 650 may connect the different components of the at least one unit controller 626. A network interface 652 may couple the at least one unit controller 626 to the network 628 via the system bus 650.

The flowcharts and step diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each step in the flowchart or step diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the step may occur out of the order noted in the figures. For example, two steps shown in succession may, in fact, be executed substantially concurrently, or the steps may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each step of the step diagrams and/or flowchart illustration, and combinations of steps in the step diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems which perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown and that the invention has other applications in other environments. This application is intended to cover any adaptations or variations of the present invention. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described herein. 

1. A method of controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the method comprising: providing at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device and at least one flow control device; utilizing a mass flow control system, wherein utilizing the mass flow control comprises the steps of: receiving a target EGR fraction comprising the portion of the exhaust stream within an inlet fluid, wherein the inlet fluid enters the inlet section of the turbomachine; determining a current EGR fraction; determining whether the current EGR fraction is within a range of the target EGR fraction; and adjusting an EGR rate of the exhaust stream if the current EGR fraction is outside of the range of the target EGR fraction.
 2. The method of claim 1, wherein the at least one constituent comprises at least one of: SOx, NOx, CO₂, O₂, water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof.
 3. The method of claim 1, wherein the step of adjusting the EGR rate of the exhaust stream comprises at least one of: adjusting a speed of the EGR flow conditioning device; adjusting a pitch of at least one EGR device; modulating at least one flow control device; or combinations thereof.
 4. The method of claim 1, wherein the step of determining the current EGR fraction comprises receiving EGR rate data from at least one EGR feedback device; and wherein EGR rate data is used to determine the current EGR fraction.
 5. The method of claim 4, wherein the at least one EGR feedback device is located adjacent the inlet section.
 6. The method of claim 1, wherein the step of determining the current EGR fraction further comprises: receiving a plurality of turbomachine operating data; and utilizing at least one energy balance for determining the current EGR fraction, wherein the at least one energy balance incorporates the turbomachine operating data.
 7. The method of claim 6, wherein the plurality of turbomachine operating data comprises at least one of the following data: compressor airflow; ambient temperature; compressor inlet temperature; exhaust stream temperature; humidity; or combinations thereof.
 8. The method of claim 1, further comprising integrating the EGR mass flow control system with at least one EGR constituent control system.
 9. The method of claim 8, wherein the step of utilizing the at least one EGR constituent control system comprises the steps of: receiving the target EGR fraction; utilizing the target EGR fraction to determine a target level of at least one constituent; determining a current level of the at least one constituent; determining whether the current level of the at least one constituent is within a constituent range; and adjusting an EGR rate of the exhaust stream if the at least one constituent is outside of the constituent range.
 10. A method of controlling an exhaust stream, wherein the exhaust stream is generated by a turbomachine; the method comprising: providing at least one exhaust gas recirculation (EGR) system comprising: at least one EGR flow conditioning device and at least one flow control device; utilizing a mass flow control system, wherein the utilizing the mass flow control comprises the steps of: receiving a target level of at least one constituent; determining a target EGR fraction; determining a current EGR fraction; determining whether the current EGR fraction is within a range of the target EGR fraction; and adjusting an EGR rate of the exhaust stream if the current EGR fraction is outside of the range of the target EGR fraction.
 11. The method of claim 10, wherein the at least one constituent comprises at least one of: SOx, NOx, CO₂, O₂, water, chloride ions, acids, aldehydes, hydrocarbons, or combinations thereof.
 12. The method of claim 10, wherein the step of adjusting the EGR rate of the exhaust stream comprises at least one of: adjusting a speed of the EGR flow conditioning device; adjusting a pitch of at least one EGR device; modulating at least one flow control device; or combinations thereof.
 13. The method of claim 10, wherein the step of determining the current EGR fraction comprises receiving EGR rate data from at least one EGR feedback device; and wherein EGR rate data is used to determine the current EGR fraction.
 14. The method of claim 13, wherein the at least one EGR feedback device is located adjacent the inlet section.
 15. The method of claim 10, wherein the step of determining the current EGR fraction further comprises: receiving a plurality of turbomachine operating data; and utilizing at least one energy balance for determining the current EGR fraction, wherein the at least one energy balance incorporates the turbomachine operating data.
 16. The method of claim 15, wherein the plurality of turbomachine operating data comprises at least one of the following data: compressor airflow; ambient temperature; compressor inlet temperature; exhaust stream temperature; humidity; or combinations thereof.
 17. The method of claim 10 further comprising integrating the EGR mass flow control system with at least one EGR constituent control system.
 18. The method of claim 17, wherein the step of utilizing the at least one EGR constituent control system comprises the steps of: receiving the target level of at least one constituent; determining a current level of the at least one constituent; determining whether the current level of the at least one constituent is within a constituent range; and adjusting an EGR rate of the exhaust stream if the at least one constituent is outside of the constituent range. 